Fix installation of Abimo

[MRigal]

If Abimo was not installed before, there is no chance that it succeeds currently.

Easy fix for Windows:
The script checks for version 3.3.0, but then installs 3.2.2, see https://github.com/KWB-R/kwb.abimo/blob/master/R/install_abimo.R#L22
I would advise to use a "global-ish" variable to store the "recommended" version to avoid these problem in the future.

Also, it enforces a "win64" platform, which is problematic to be ran on a server (Linux) or a Mac OS software. See https://github.com/KWB-R/kwb.abimo/blob/master/R/install_abimo.R#L16
Ideally, the original packages Abimo should be available for all main platforms.

In the meantime, the R package should identify the operating system using something like https://stat.ethz.ch/R-manual/R-devel/library/base/html/Sys.info.html and for non-windows platform warn that it cannot be installed automatically but hint that the software should be built from source and then linked with the fitting suffix in the R-site-library folder.

[hsonne]

Regarding the version number mismatch now, since #14, the version number is returned by a function.